I wouldn't do it looking at your roster - you could use a RB but you need Julio as well. I'd probably keep Julio and try and secure a RB with the 1.04. Or try and trade for a young upside RB who wouldn't be as expensive (ie Ingram, Ridley/Vereen, Helu/Royster, Jacquizz Rodgers, those types, all of whom I like a lot.)

When is your rookie draft? If you can get Blackmon with that #4 pick, I think it makes a lot of sense to deal Julio for Foster (and I love Julio). I'd rather have Foster and Blackmon than Julio and Martin myself. It's tempting even without Blackmon.

I only worry bout mcfaddens ability to shoulder the load, still only 24 and now is the main man with bush gone.

Then grab McFadden, it's fair for Marshall for sure. But I'd go the NE route as I think one of Ridley/Vereen is going to be really good and this is the time to get them, before they bust out.
But McFadden/Marshall is a fair deal.